For a club of Manchester United’s stature and expectations, not every talented young player can make the grade. Only the exceptional succeed in nailing down a regular spot and establishing themselves as first-team stars across multiple seasons. See those ‘Fergie Fledgings’ David Beckham, Gary Neville, Paul Scholes and Ryan Giggs. See ‘Ten Hag’s Tots’, the FA Cup-winning heroes Kobbie Mainoo and Alejandro Garnacho. For every Mainoo, for every Scholes, however, there are countless others who fall just short. But, as far as academy director Nick Cox is concerned, Manchester United have a duty not…